737 Flight Crew Operations Manual
Flight Controls -
System Description
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9.20.10 D6-27370-866-EGP
Stall Identification
Stall identification and control is enhanced by the yaw damper, the Elevator Feel
Shift (EFS) module and the speed trim system. These three systems work together
to help the pilot identify and prevent further movement into a stall condition.
During high AOA operations, the Stall Management/Yaw Damper (SMYD)
reduces yaw damper commanded rudder movement.
The EFS module increases hydraulic system A pressure to the elevator feel and
centering unit during a stall. This increases forward control column force to
approximately four times normal feel pressure. The EFS module is armed
whenever an inhibit condition is not present. Inhibit conditions are: on the ground,
radio altitude less than 100 feet and autopilot engaged. However, if EFS is active
when descending through 100 feet RA, it remains active until AOA is reduced
below approximately stickshaker threshold. There are no flight deck indications
that the system is properly armed or activated.
As airspeed decreases towards stall speed, the speed trim system trims the
stabilizer nose down and enables speed trim above stickshaker AOA. With this
trim schedule the pilot must pull more aft column to stall the airplane. With the
column aft, the amount of column force increase with the onset of EFS module is
more pronounced.
September 15, 2016
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